Answer:
A and C
Step-by-step explanation:
I had it on a test
The function in vertex form is
(refer to your other post I solved it there).
The general form of quadratic equations in vertex form is
, where (h, k) is the vertex of the parabola.
Here, a = 1, h = -6 and k = -54
Therefore, the vertex is (-6, -54) and it is a maximum because a = 1 is postive.
OK, so the graph is a parabola, with points x=0,y=0; x=6,y=-9; and x=12,y=0
Because the roots of the equation are 0 and 12, we know the formula is therefore of the form
y = ax(x - 12), for some a
So put in x = 6
-9 = 6a(-6)
9 = 36a
a = 1/4
So the parabola has a curve y = x(x-12) / 4, which can also be written y = 0.25x² - 3x
The gradient of this is dy/dx = 0.5x - 3
The key property of a parabolic dish is that it focuses radio waves travelling parallel to the y axis to a single point. So we should arrive at the same focal point no matter what point we chose to look at. So we can pick any point we like - e.g. the point x = 4, y = -8
Gradient of the parabolic mirror at x = 4 is -1
So the gradient of the normal to the mirror at x = 4 is therefore 1.
Radio waves initially travelling vertically downwards are reflected about the normal - which has a gradient of 1, so they're reflected so that they are travelling horizontally. So they arrive parallel to the y axis, and leave parallel to the x axis.
So the focal point is at y = -8, i.e. 1 metre above the back of the dish.
Answer:
a. S = 3n + 2
b. There while be 62 squares.
Step-by-step explanation:
We know the first term of this sequence is 5. To figure out the equation, subtract the following term from the previous. Do you see a common difference?
8 - 5 = 3
11 - 8 = 3
14 - 11 = 3
We're seeing a constant difference of 3 (which makes this an arithmetic sequence), but the first term is 5. That mean something is being added to make the first term 5. Subtract 3 from 5 to get 2. This means 2 is being added to every multiple of 3, which leads us to the equation: S = 3n + 2.
To find the 20th term of this sequence, substitute n for 20 and do the operations.
S = 3(20) + 2
<em>Multiply 3 by 20, then add 2.</em>
S = 62
The 20th term will have 62 squares.
